The measurement of the steering angle and a respective change in the vehicle steering angle is of great importance for the dynamic regulation of vehicles. Various measuring principles can be used for the determination of the steering wheel angle, corresponding to the steering angle. Digital optical processes include discrete transmitting and receiving modules as well as charge-coupled device modules. Magnetically sensitive components include Hall elements. In Zeitschrift Antriebstecnik, Vol. 33 (1994) Issue No. 7, pp. 28-29, a resolver has been described as an additional sensor for the angle of rotation which can be used for the mechanical design of tools, robots, printing presses, packaging machines, etc.
Resolvers consist, in principle, of a rotor and a stator. A sinusoidal magnetic field is generated at the rotor which rotates along therewith. This field induces voltages in two phase windings of the secondary stator winding which are a function of the rotational position of the rotor. In order to obtain sine and cosine signals, the two phase windings of the stator are offset by 90xc2x0. In the case of the conventional resolver, the transmission of electrical energy is accomplished with the aid of a coupling transformer. This consists of two concentric windings: a primary winding mounted in the stator housing and a secondary winding located on the rotor, with which it rotates. The secondary winding feeds the sine-generating winding via two conductors to the rotor. Novel developments without wiper contacts have been proposed. More exact information in this regard is given in the above cited article.
It is the object of the present invention to introduce a novel measuring device for the measurement of the vehicle steering angle which is able to specify the absolute angle of rotation and which is very robust with regard to design. A resolver of the type described above is therefore used in accordance with the invention for the measurement of the vehicle steering angle and the respective change in the vehicle steering angle. The resolver contains a stator with three windings. There is a field winding as a primary winding and two secondary windings mutually offset by 90xc2x0. The rotor may also be equipped with an auxiliary winding or with magnetic materials. By means of an evaluation circuit, which can be obtained as a single integrated circuit (IC) from Analog Devices, e.g., the absolute value of the angle of rotation is determined by input of a constant frequency signal, for example 10 kHz, and by evaluation of the voltage induced in the two 90xc2x0 offset secondary windings.
The use of a resolver in the measuring device in accordance with the invention offers a number of advantages, wherein an identification of the absolute value of the angle between 0xc2x0 and 360xc2x0 is possible. The measured values can be specified precisely to 13 bits without difficulty, which corresponds to a resolution of 0.05xc2x0. Furthermore, the resolver is free of interference with respect to temperature, dirt, mechanical vibration and has good electromagnetic performance. Also, the physical dimensions of the resolver can be well adapted to the prevailing requirements of a vehicle.
As was already described in connection with other steering angle sensors, the steering angle sensor according to the invention can also be integrated into the steering column assembly switch. The rotor must be integrally coupled to the rotatable steering rod and the stator can be mounted to the steering column tube.
The measuring device according to the invention facilitates an additional central option of providing wireless signal transmission, in the most general sense, between devices in the vehicle mounted rigidly with respect to the chassis and devices rotatable with the steering wheel. For this purpose, special rotary connectors were previously used which transmitted the signals via helical springs or coiled flat-band cables (so-called coil springs) between the steering wheel and the devices fixed with respect to the chassis. A wiper contact was also used in connection with such signal transmission. The present invention now makes use of the fact that an inductive coupling is present between the rotor connected to the steering wheel and the stator. It is therefore possible to exchange signals between the rotor and the primary and/or the secondary winding of the stator using this inductive coupling. The signals can thus arrive at the steering wheel in order to trigger an actuator for an air bag, for example, and may also be conducted away from the steering wheel, in order, e.g., upon activation of a horn contact, to bring a control signal to the horn rigidly mounted with respect to the chassis. In this manner, either control signals or control information can be fed toward the steering wheel and into the stator winding or be transmitted in the opposite direction. The control signals are passed to a winding connected to the steering column and further processed in an electronic circuit for the control of devices located on the steering wheel and corresponding signals coming from the steering wheel are transmitted in order to be able to activate, from the steering wheel, devices rigidly mounted with respect to the chassis.
In addition to the transmission of information signals for driving individual devices, the invention is also suitable for supplying power to operate changeover switches connected to the steering wheel.
Since the individual signals must not interfere with one another or become superimposed, the invention proposes that these individual signals be transmitted sequentially in time via the resolver or that separate frequency channels be provided for the signals being transmitted. Thus, for example, a frequency of 10 kHz can be provided for the measurement of the angle of rotation itself, while a frequency band lying above this frequency can be used for the transmission of the other signals. In this manner, several time-multiplexed or frequency-separated channels are created in the resolver so that it can deal with the different objectives described above. A combination of these measures is also possible.
The devices connected to the steering wheel can include, for example, a triggering circuit for an air bag or a control circuit for activating electrical devices, wherein the electrical devices can be rigidly mounted in the vehicle with respect to the chassis, e.g. an auto horn, a radio, or vehicle lights. According to the above-described system, control signals generated at the steering wheel can be transferred for various devices without contact and in a reliable fashion via the resolver. In principle, not only can the individual signals be assigned to different frequency bands or transmitted in time-multiplexed fashion, but only a single information signal can also be used which is encoded to transmit different information. The information signals can thereby be transmitted or exchanged between the steering wheel and the devices in the vehicle, rigidly fixed with respect to the chassis. Various information present on the car information network (CAN) can therefore be transmitted, without contacts, to provide a CAN transmission and return path to the steering wheel.
An encoding can occur with the aid of a central electronic circuit that is arranged at the input or output of the stator windings or at the input or output of the rotor winding. In particular, information can, for example, be transmitted for ignition of the air bag ignition pellet when the sensors of the vehicle have determined a corresponding presence of danger.
The stator can comprise a primary winding and two auxiliary or secondary windings that are connected in the manner of a transformer. A rotor with a rotor coil is particularly important with respect to the resolver. The position of this winding influences the amplitude of the signals at the secondary windings such that, on the basis of these signals, the rotational position of the rotor can be deduced. The secondary windings are rotated through 90xc2x0 with respect to one another so that the induced voltages correspond to the sine and cosine of the rotor angle. More precise details can be deduced from the 1994 prospectus of Admotec Prxc3xa4zision AG, Kxc3xcssnacht/Switzerland, in which a rotor is described in detail.
The signal transmission between the rotor coil connected to the steering wheel and the stator windings can be time- or frequency-multiplexed. The auxiliary windings of the stator determine the angle of rotation xcex1 using a frequency of 10 kHz and via a low-pass filter. In addition thereto, various information coming from the steering wheel can also be supplied into the winding. This can occur at frequencies which lie sufficiently above or below the frequency for measurement of the angle of rotation. For example, the information from a sensor on the steering wheel or a switch setting can serve as steering wheel information which is converted into suitable frequency signals in the steering wheel circuit. These signals can then be detected by the windings of the stator using an appropriate filter, (e.g. a band-pass filter) as well as a first stator circuit and either supplied to the electronic CAN or used directly to trigger actuators (horn, blinkers, radio). In the opposite direction, sensor information or information from the CAN can be converted into frequencies appropriate to the filter, so that this information can be processed by a steering wheel circuit and evaluated for triggering suitable actuators (for example, the ignition pellet for the air bag).
A generator can supply the frequency to the primary winding which is necessary for activation of the resolver to measure the angle of rotation.
The power for the steering wheel circuit can also be supplied to the steering wheel without contacts via the windings of the resolver. The central circuit and parts of the resolver itself (stator) can be integrated into a steering column assembly switch. Via the central circuit, switch states of the steering column assembly switch can be transmitted via the CAN bus to the electrical devices rigidly disposed with respect to the chassis.
The information for angle identification (at a frequency of 10 kHz) and the remaining switch information can also be transmitted in time-multiplexed fashion.
When the information relating to the angle of rotation is processed at a frequency of 10 kHz, a band-pass filter operating in a higher range of frequencies can be used for secure transmission of the switch information.
An embodiment of the invention will now be described with reference to the drawing.